The effects of laser energy and atmosphere on the emission characteristics of laser-induced plasmas were studied with the use of a Q-switched Nd: YAG laser over a laser energy range of 20 to 95 mJ. Argon, helium, and air were used as surrounding atmospheres, and the pressures were changed from atmospheric pressure to 1 Torr. The experimental results showed that the maximum spectral intensity was obtained in argon at around 200 Torr at a high laser energy of 95 mJ, whereas the line-to-background ratio was maximized in helium at around 40 Torr at a low energy of 20 mJ. The results are discussed briefly on the basis of the temporal and spatial observations of the laser-induced plasmas.
The effect of the laser energy on the intensity of the spectrum of a Q-switched laserinduced plasma in different reduced atmospheres, Ar, He, and air was studied by changing the laser pulse energy over a range of 20 to 95 mJ. At low pressure, the emission intensity increases linearly with increasing the laser energy for three kinds of gases. However, at high pressure near atmospheric pressure, the more intense emission intensity can be obtained by increasing the laser energy for He, while for Ar and air, higher laser energy does not bring about high emission intensity. The cause for this is discussed briefly in terms of the gas breakdown and self-absorption. 1.
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